Electrical unit and terminal lead connection therefor



July 12, 1966 B. L. WELLER ETAL 3,260,907

ELECTRICAL UNIT AND TERMINAL LEAD CONNECTION THEREFOR Original FiledJune 19, 1962 &

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g g/wand A- BoZ ATTORNEYS United States Patent 3,260,907 ELECTRICAL UNITAND TERMINAL LEAD CONNECTION THEREFOR Barton L. Weller, Monroe, andEdmund A. Bolton, Easton, Conn., assignors to Vitramon, Incorporated,Monroe, C0nn., a corporation of Delaware Original application June 19,1962, Ser. No. 203,600. Divided and'this application Sept. 26, 1963,Ser. No. 311,736

7 Claims. (Cl. 317-261) This application is a division of our co-pendingapplication Serial No. 203,600, filed June 19, 1962.

This invention relates to terminal lead connections for electricalunits. More specifically, it constitutes an impvovement on the terminallead connection disclosed in the US. patent of Barton L. Weller, No.3,021,589.

In the aforesaid patent a terminal lead connection for an electricalunit having a substantially rigid moonlithic body formed of superposed,substantially parallel layers of material having specific electricalcharacteristics, including at least one electrically conductive layerlying wholly within the body is disclosed wherein the terminal leadextends into the body transversely of the layers so that it haselectrical connection with the electrically conductive layer, the leadbeing gripped by the body which is shrunk thereon during the finalcuring of the body.

According to the invention of the said patent, the lead is received in arecess formed in the body, extending at least through the electricallyconductive layer thereof, which is initially of a diameter sufficient toreceive the lead, yet is small enough to enable the body to shrink intogripping engagement therewith. The lead has electrical connection withthe electrically conductive layer exposed by the recess and, while suchconnection might constitute direct engagement of the lead and theelectrically conductive layer, in the preferred form an electricallyconductive lining on the wall of the recess is engaged by the lead forconnecting the lead to the electrically conductive layer. The lining,which is bonded to the electrically conductive layer and to the lead, inaddition to forming the electrical connection between the two alsofunctions, in units wherein the electrode comprises a plurality ofplates or electrically conductive layers, to electrically tie the platestogether to form the electrode.

While Patent No. 3,021,589 provides a terminal lead connection to anelectrode, having a part thereof at least disposed wholly within thebody of an electrical unit, a number of problems have been encounteredwhich directly affect the reliability of the unit, such problemsresulting from reduced mechanical strength and electrical continuity ofthe lead connection.

It has been found that high stresses, resulting from manipulation of thelead, exist at the juncture or interface of the relatively soft metallead and the rigid body. These stresses, which are greater than thetensile strength of the malleable lead metal, tend to cause the lead tomove and distort at the point of stress, such distortion resulting in arupture of the electrical connection between the lead and theelectrically conductive layer. The rupture, which may occur in the bondbetween the lead and the layer and/or between the lead and theelectrically conductive lining, depending on the construction of theparticular unit, is progressive, usually starting at the outermost pointof bond and propagating downwardly into the recess with each subsequentstressing of the lead. Consequently, a terminal lead connection, whichwas originally mechanically strong and electrically reliable, underrepeated stressing, will fail as a result of the inability of the bondto absorb the movement of the malleable lead and transmit it to therelatively rigid body of the unit.

The present invention overcomes the problems aforenoted and has as animportant object thereof to provide a terminal lead connection in anelectrical unit which includes a bond at the juncture of the relativelysoft lead and rigid body that is capable of withstanding normalstressing of the lead without rupturing.

According to the invention, the aforesaid object is achieved byproviding a cushion or malleable bond at the juncture of the lead andbody, the bond having sufficient malleability to distribute the stresson the lead and spread it around its entire periphery, so that, at anygiven point, it is held below the tensile limits of the lead and lead tobody interface area.

In one form. of the invention the provision of the malleable bond isaccomplished by forming the leadreceiving recess in the body ofsubstantially greater diameter than the lead to be inserted therein sothat a substantial thickness of shock absorbing bonding material can bedisposed therearound for absorbing and distrib uting stresses.

It is also an object of the invention to provide a terminal leadconnection in an electrical unit which includes means for distributingstress, resulting from manipulation of the lead, around the entireperiphery of the lead in the interface area with the unit body so thatat any given point in the interface area the stress does not surpass thetensile strength of the lead or the lead to body bond.

Another object of the invention is to provide a terminal lead connectionhaving means for cushioning the bond or connection against rupture whilemaintaining electrical connection between the lead and the electrodethat lies wholly within the body of the electrical unit.

Still another 'object of the invention is to provide a terminal leadconnection in an electrical unit which includes a substantial thicknessof shock absorbing bonding material between the lead and the body in theinterface area, the bonding material being electrically conductive forelectrically connecting the lead to the electrode of the unit whilecushioning the juncture of the lead and body against rupture.

Still another object of the invention is to provide a terminal leadconnection in an electrical unit between a relatively soft metal leadand rigid body which is electrically reliable, mechanically strong andfree of areas of concentrated stress resulting from lead manipulation.

It is further an object of the invention to provide a capacitor unit,having a terminal lead connection according to the invention.

Other objects and advantages will be apparent from the specification andclaims, when considered in connection with the attached sheet ofdrawings, illustrating one form of the invention, wherein likecharacters represent like parts and in which: I

FIGURE 1 is a fragmentary elevational view, in section, of a capacitorunit in accordance with the invention and just prior to insertion of thelead therein;

FIG. 2 is the same as FIG. 1, but shows the lead in inserted position;

FIG. 3 is a fragmentary plan View of the capacitor unit of FIG. 2; and

FIGS. 4 through 7 are each fragmentary elevational views, in section, ofa capacitor unit having a modified form of terminal lead connectionaccording to the invention.

Referring now to the drawings for a more detailed description of theinvention, in FIGS. 1 to 3 an electrical unit 10 is shown at variousstages in the formation of the terminal lead connection according to theinvention. While the concepts of the invention are applicable tocapacitors, resistors, inductors and similar electrical devices having aporcelain, glass, ceramic or other substantially rigid monolithic bodyin which a part, at least, of the electrodes lie wholly within the body,in the herein illustrated form of the invention, for purposes ofdescrip- 3 tion, a capacitor of the type disclosed in US Patent No.3,021,589 is shown.

Reference may be made to the said patent for particular details ofconstruction of the capacitor, however, for present purposes it issufficient to note that it comprises a substantially rigid monolithicbody 11 of superposed substantially parallel layers of dielectricmaterial 12 and electrically conductive material 13, the latter formingthe electrode plates of the unit and lying wholly within the body. Whilein some instances it may be desired to have additional electrode plateson the exterior of the body and connected to the interior plates, it ispresently preferred and herein illustrated as having all of theelectrode plates disposed wholly within the body.

The electrically conductive layers or plates 13 of body 11 are, as iswell understood in the art, spaced by a layer or layers of thedielectric material 12 and so formed as to define two electricallydistinct groups of electrode plates 14 and 15. The groups of electrodeplates, which each form one electrode of the capacitor unit may beformed by any means known to the art, including relatively displacingadjacent plates so that alternate plates overlie one another orproviding a cutout or the like at the opposite ends of adjacent platesso that the cutouts of alternate plates are in corresponding positions,to facilitate electrically connecting all of the plates of each group toform its respective electrode.

Heretofore, terminal lead connections have been made in the electricalunit with each of the electrodes 14 and 15 of the unit by inserting aterminal lead means into the body for establishing electrical connectionwith its respective electrode and communicating it outwardly of thebody. According to the prior art, insertion of the terminal lead meansinto the body is achieved by forming a recess in the body sufficientonly to receive the lead so that on curing the body it is able to shrinkinto engagement with the lead for gripping the same. The lead in suchprior art constructions had either direct electrical contact with theelectrically conductive layer or layers of the body or had electricalconnection therewith through an electrically conductive lining disposedon the wall of the recess. As will be readily understood, theelectrically conductive lining, in addition to connecting the lead toits respective electrode, functioned to tie the plates forming theelectrode together if required.

It has been found that terminal lead connections of the aforementionedtype tended to rupture at the interface or bond between the lead and thebody of the unit as the result of stresses due to manipulation of thelead. The stressing of the lead, which is soft and malleable relative tothe rigid monolithic body of the device, overcomes the tensile strengthof the lead and the bond, eventually rupturing the same and causingelectrical and mechanical breakdown of the unit.

According to the present invention, this problem is overcome and ahighly reliable terminal lead connection is formed by providing acushion between the lead and the body for distributing the stressesentirely around the periphery of the lead so that at any given point thestress is no greater than the tensile strength of the lead or theinterface bond.

In FIGS. 1 through 3 one method of providing the desired cushion isshown according to the invention. A recess 16, which is formed in amanner similar to that disclosed in the prior art, is provided. In thepresent invention, however, the recess, rather than being of a size onlysufiicient to receive the lead, is of substantially greater diameterthan the lead to be inserted therein for receiving a shock absorbingbonding material between the inserted lead and the wall of the recess,as will be hereinafter described. While the diameter of the recess 16 inrelation to the diameter of the lead may vary, depending on the tensilestrength of the lead or interface bond, it has been found desirable toform the recess of a diameter approximately twice that of the lead,thereby enabling a cushion of the shock absorbing bonding material to bedisposed between the lead and the wall of the recess equal toapproximately the radius of the lead.

After the recess 16 has been formed it is lined with electricallyconductive material 17, of any type and in any manner well known to theart, for electrically engaging all of the electrode plates exposed bythe recess and tying them together to form one of the electrodes of theunit. Thereafter, the body is cured to harden the layers into a rigidmonolithic body and secure the lining in position.

After the body has been cured, but not necessarily immediatelythereafter, a quantity of silver or other electrically conductive solder13, of any well known type, is inserted in the recess, as shown inFIG. 1. A lead 19, as shown in FIG. 2, is then inserted in the recess sothat it is substantially centered and the solder flows therearound toform a shock absorbing cushion of substantial thickness between the leadand the wall of the recess. While the lead 19, within the concepts ofthe invention, may be circular or square in cross-section, or of anyother configuration, in the form of the invention shown in FIGS. 1 to 3the lead is spa-ded, as at 20, to prevent its turning and eliminatepiston effect as it is inserted. The solder 18 in addition to cushioningthe lead by absorbing stresses imparted thereto, electrically connectsthe lead to the lining 19 so that the lead has electrical connectionwith the electrode for communicating it outwardly of the body.

It should here be noted that the foregoing has the additional advantageof enabling the lead to be inserted in the body after the body is curedthus enabling leads of any desired material to be utilized since thelead will be unafiected by the curing operation. Further, the curedbody, prior to insertion of the lead into the recess, may be stored forinventory, shipped or otherwise handled, thereby reducing over-allinventory and cost.

In FIGS. 4 through 7 modified forms of terminal lead connections withinthe concepts of the invention, are shown, all being illustrated inconnection with a capacitor or electrical unit 10 of the type describedin connection with FIGS. 1 to 3. In these embodiments of the inventionthe lead wire 19 is shown as being circular in crosssection.

In FIG. 4 a sleeve or liner 21 of electrically conductive material isdisposed in the recess 16 between the electrically conductive lining 17and the bonding material 18. The liner, which is adapted to assurereliable, mechanical and electrical connection between the electricallyconductive bonding material and the Lining on the wall of the recess, ispositioned in the recess prior to curing the body so that the body willshrink thereon during the curing operation to grip it and retain it inposition. In connection with the liner 21, it should be noted that inmany cases the liner has been found necessary for assuring electricalconnection between the bonding material and the electrically conductivelining on the wall of the recess since the glaze produced by the flux inthe lining has a tendency to interefere with the desired electricalbond; the liner overcomes this problem and provides a readilysolderaible surface.

In FIG. 5 the terminal lead connection is made in the same manner as wasdescribed with respect to FIGS. 1 to 3 through the curing operation.However, at this point a non-conducting shock absorbing bonding material22, such as any well known epoxide resin is inserted in the recess andthe lead is thereafter positioned to bottom in the recess as shown at 23for physically contacting and engaging the lining 17 on the wall of therecess. In this construction the bonding material 22 serves only toretain the lead in position and cushion it against stress, theelectrical contact between the lead and the electrode bein g independentof the bonding material.

In FIG. 6 the terminal lead connection shown is identical to thatdescribed in FIGS. 1 to 3 except that the shock absorbing bondingmaterial, rather than being an electrically conductive silver solder orthe like, comprises an electrically conductive epoxide resin 24. Theelectrically conductive epoxide resin, while it may take any form knownto the art, in the illustrated and preferred form of the inventioncomprises a suspension of silver or similar conducting particles 25 andepoxide resin.

In FIG. 7 the terminal lead connection is made by inserting a quantityof shock absorbing bonding material 26, formed of electricallyconductive epoxide resin similar to that described with respect to FIG.6, in the recess so that a portion, at least, of the wall of the recessis lined with the bonding material, it being necessary that all of theelectrode plates exposed by the recess are engaged by the bondingmaterial. Thereafter the lead 19 is inserted in the same manner as wasdescribed with respect to the other forms of the invention so that asubstantial thickness of the bonding material is disposed around thelead for cushioning the same. In this form of the invention the lead 19has electrical connection with its respective electrode of the unitthrough the electrically conductive epoxide resin forming the bondingcushion 26.

Thus, among others, the several objects and advantages of the inventionas aforenoted are achieved. Obviously numerous changes in the structuremay be resorted to without departing from the spirit of the invention asdefined by the claims.

We claim:

1. In an electrical component which includes a substantial-1y rigidmonolithic body formed of substantially parallel layers of materialhaving specific electrical properties, at least one of said layers beingelectrically conductive and lying wholly Within said body, and aflexible terminal lead extending into said body and having electricalconnection with said electrically conductive layer for electricallycommunicating the same outwardly of the body; the improvement whereinsaid terminal lead is disposed in a recess extending into said body atleast to said electrically conductive layer, said recess being ofsubstantially greater diameter than said lead so that an annular spaceis provided between the lead and the body, and a shock absorbing bondingmaterial is disposed in said annular space for forming an annularcushion around said lead and bonding the same in position, said leadhaving electrical connection with said electrically conductive layer andsaid cushion increasing the eflective surface area of the bond relativeto the surface area of the bonded portion of the lead, whereby stressresulting from flexing of the lead is dissipated.

2. In an electrical component which includes a substantially rigidmonolithic body formed of substantially parallel layers of materialhaving specific electrical properties, at least one of said layers beingelectrically conductive and lying wholly within said body, and aflexible terminal lead extending into said body and having electricalconnection with said electrically conductive layer for electricallycommunicating the same outwardly of the body; the improvement whereinsaid terminal lead is disposed in a recess extending into said body atleast to said electric-ally conductive layer, said recess having adiameter approximately twice the diameter Olf said lead so that anannular spaceis provided between the lead and the body approximatelyequal to the radius of said lead, and a shock absorbing bonding materialdisposed in said annular space for forming an annular cushion aroundsaid lead and bonding the same in position, said lead having electricalconnection with said electrically conductive layer and said cushionincreasing the effective surface area of the bond relative to thesurface area of the bonded portion of the lead, whereby stress resultingfrom flexing of the lead is dissipated.

3. in an electrical capacitor which comprises a substantially rigidmonolithic body formed of substantially parallel layers of materialhaving specific electrical properties, said layers including a pluralityof dielectric layers and a plurality of electrically conductive layers,at least some of said electrically conductive layers lying whollywithinsaid body, said dielectric layers separating said electricallyconductive layers, means electrically connecting alternate electricallyconductive layers for forming electrodes of opposite polarity, and aflexible terminal lead for each electrode extending into said body andhaving electrical connection with said electrical connecting means forelectrically communicating its respective electrode outwardly of thebody; the improvement wherein said terminal leads each are disposed in arecess extending into said body at least through said electricallyconductive layers forming its respective elect-rode, said electricalconnecting means comprising a lining on the wall of said recess, saidrecesses each being of substantially greater diameter than itsrespective lead so that an annular space is provided between said leadand the body, and a shock absorbing bonding material is disposed in saidannular spaces for forming an annular cushion around said lead andbonding the same in position, said leads each having electricalconnection with their respective electnical connecting means and saidcushions increasing the effective surface area of the bonds relative tothe surface area of the bonded portion of the leads, whereby stressresulting from flexing of the leads is dissipated.

4. A terminal lead connection to an electrically conductive elementwholly embedded in a substantially rigid monolithic body comprising aflexible terminal lead wire disposed in a recess in said body extendingat least into said electrically conductive element therein, said recessbeing of substantially greater diameter than said lead wire so that anannular space is provided between said lead wire and said body, and ashock absorbing bonding material disposed in said annular space forforming an annular cushion around said lead wire and bonding the same inposition, said lead wire having electrical connection with said elementand said cushion increasing the effective surltace area of the bondrelative to the surface area of the bonded portion of the lead wire,whereby stress resulting from flexing of the lead wire is dissipated.

5. A terminal lead connection as defined in claim 4, wherein said recesshas a diameter approximately twice the diameter of said lead wire sothat said annular space between the lead wire and the body isapproximately equal to the radius of the lead wire.

6. The invention defined in claim 1 wherein said shock absorbing bondmaterial comprises an electrically conductive epoxide resin and haselectrical connection With said electrically conductive layer, said leadhaving electrical connection with said electrically conductive layerthrough said bonding material.

7. The invention defined in claim 3 wherein there is an electricallyconductive sleeve means for each elect-rode positioned between saidbonding material and said means for connecting alternate electricallyconductive layers, said leads having electrical connection with theirrespective layer connecting means through said sleeve means.

References Cited by the Examiner UNITED STATES PATENTS 2,389,018 11/1945Ballard. 2,413,539 12/1946 Ballard 339-275 X 2,502,291 3/1950 Taylor.3,007,997 11/1961 P'anariti 339-17 X 3,021,589 2/1962 Weller 317242 XOTHER REFERENCES Lorenz, E. 1.: Card Reading Plate, IBM TechnicalDisclosure Bulletin, vol. 1, No. 3, October 1958, page 1.

LARAMIE E. ASK IN, Primary Examiner.

JOHN F. BURNS, Examiner.

D. J. BA'DER, Assistant Examiner.

4. A TERMINAL LEAD CONNECTION TO AN ELECTRICALLY CONDUCTIVE ELEMENT WHOLLY EMBEDDED IN A SUBSTANTIALLY RIGID MONOLITHIC BODY COMPRISING A FLEXIBLE TERMINAL LEAD WIRE DISPOSED IN A RECESS IN SAID BODY EXTENDING AT LEAST INTO SAID ELECTRICALLY CONDUCTIVE ELEMENT THEREIN SAID RECESS BEING OF SUBSTANTIALLY GREATER DIAMETER THAN SAID LEAD WIRE SO THAT AN ANNULAR SPACE IS PROVIDED BETWEEN SAID LEAD WIRE AND SAID BODY, AND A SHOCK ABSRBING BONDING MATERIAL DISPOSED IN SAID ANNULAR SPACE FOR FORMING AN ANNULAR CUSHION AROUND SAID LEAD WIRE AND BONDING THE SAME IN POSITION, SAID LEAD WIRE HAVING ELECTRICAL CONNECTION WITH SAID ELEMENT AND SAID CUSHION INCREASING THE EFFECTIVE SURFACE AREA OF THE BOND RELATIVE TO THE SURFACE AREA OF THE BONDED PORTION OF THE LEAD WIRE, WHEREBY STRESS RESULTING FROM FLEXING OF THE LEAD WIRE IS DISSIPATED. 